A risk assessment perspective on the neurobehavioral toxicity of endocrine disruptors

Agents that alter the functional properties of endocrine systems pervade the environment. Their full implications for public health and ecological integrity, however, may not be captured by labels such as "disruptor" because their actions ramify in so many directions. The process by which we describe and evaluate such actions, risk assessment, is also the means by which society judges their significance. It determines the allocation of resources to their investigation and, potentially, control. A full, formal, risk assessment endeavor, in the detail applied to cancer evaluation, still awaits application to endocrine disruptors, however. It will not be as transparent a process because, unlike the conventional risk model based on carcinogens, identification of a chemical as an endocrine disruptor, as is true of neurobehavioral toxicants in general, will not trigger a virtually automatic sequence of policy steps. The primary distinction between cancer and endocrine disruptors and neurotoxicants is the plethora of possible endpoints by which toxicity can be expressed. Cancer is a unitary index. Adverse consequences flowing from exposure to endocrine disruptors can take an almost infinite variety of forms, including neurobehavioral outcomes. In their most troubling manifestations, these emerge as disorders of early development. They can range from deviant patterns of male copulatory behavior to impaired cognitive function. Each of these indices, in turn, exhibits multiple dimensions. Moreover, some aftermaths, as with cancer, might emerge only after long latencies. Different stages of the life cycle following developmental exposure will manifest different outcomes as a consequence. Some adverse effects may arise for the first time in advanced age because it is a period of declining compensatory margins. These multiple facets of neurobehavioral toxicity, and, by extension, their coupling to endocrine disruptors, imply a risk assessment process that corresponds, in many ways, to the global views adopted by ecotoxicologists.